1. Field of the Invention
The present invention relates to a method of manufacturing a window having at least one of a radio wave stealth property and an electromagnetic wave shield property that is applicable to aircraft or the like, in particular to stealth aircraft, and to a window material having at least one of a radio wave stealth property and an electromagnetic wave shield property.
This application is based on patent application No. 2003-340497 filed in Japan, the content of which is incorporated herein by reference.
2. Description of Related Art
In the past, a window member composed of a transparent resin or inorganic glass with a transparent conducting film such as gold or ITO (indium tin oxide) coated thereon, as an electromagnetic wave shield window used for aircraft, in particular for stealth aircraft, is known. Applying such transparent conducting film enables, while maintaining transparency to visible radiation, both a radio wave stealth property which scatters radio waves in various directions so as not to be detected by radar, and an electromagnetic wave shield property which prevents harmful electromagnetic waves, except for visible radiation, from invasion into an aircraft.
However, in many cases, such window members for aircraft, especially windshields and canopies are bent at a large curvature and have a multiple curved surface shape, having a plurality of radius of curvature. Therefore there is a problem in that it is difficult to coat a transparent conducting film on a window member in a uniform thickness.
There is yet another problem in that as the radio wave stealth property or the electromagnetic wave shield property is increased, the transparency to visible radiation is reduced. In particular, to achieve an adequate radio wave stealth property or electromagnetic wave shield property with a transparent conducting film, the transmissivity of visible radiation drops to 70% or lower, which causes a problem in that the view from the aircraft is darkened.
Furthermore, a window having at least one of a radio wave stealth property and a electromagnetic wave shield property, comprising a window member coated with a transparent conducting film, is exposed to a wide range variation in outside pressure and temperature during flight and the window member deforms.
However, the transparent conducting film, especially ceramic transparent conducting film such as ITO does not deform sufficiently to follow the deformation of the window material. Therefore the transparent conducting film might crack even with relatively little deformation, which can occur during an actual flight. To prevent such cracking, especially ceramic transparent conducting film such as ITO is coated on the inner side of the windows, which deform relatively less.
On the other hand, a front filter applied to a plasma display panel, which is in a totally different field of art compared to aircraft windows, is known as a device to shield harmful electromagnetic waves and let only visible radiation go through.
For example, in Japanese Unexamined Patent Application, First Publication No. 2001-189589 (from paragraph [0003] to [0004] and FIG. 3) there is disclosed a front filter of a construction where a resin film of for example PET (polyethylene terephthalate) formed with a conductive mesh thereon, is adhered integrally so as to cover the whole front side of a plasma display panel.
However, such a front filter is essentially flat because it is supposed to be applied to a plasma display panel. Therefore, it is difficult to apply such a front filter to a window having a multiple curved surface shape such as for an aircraft canopy.